Abstract The martensitic transformation of Cu-Zn-Al- single crystals has been followed in situ and in real time by synchrotron X-ray topography. We have shown that at the Ms temperature, the transformation proceeds by nucleation and growth of transformation variants associated by self-accomodating pairs. The nucleation of these variants is triggered by the crystal substructure. When the transformation is multivariant we have displayed the development of elastic stresses, accompanying the growth of variants, inducing a reversible curvature of the lattice planes.